LEGO mill produces sculpted models with fantastic resolution

[Arthur Sacek] has really got something with the 3D Mill he built entirely from LEGO pieces. As you can see, it uses NXT parts to control the cutter head along three axes. The drill bit that acts as the mill’s cutting head is not a LEGO part, but that’s [Arthur’s] only transgression.

The demo sculpture seen above was cut into a block of floral foam. The model was processed by Autodesk Softimage before being fed into the mill, where it took about two and half hours to complete the job. The foam comes out still in block form looking like a piece of outdoor carpeting. That’s because there’s no debris removal during the milling process. But hit it with the shopvac and you’ll reveal a physical model with surprising detail. We don’t think it comes close to the light-cured resin printing we’ve seen, but it would be a great asset if you’re doing some mold making.

@dgent — it’s sturdy enough for you to carefully make a mold from brushed-on RTV silicone. If you sprayed the surface with something hard like cyanoacrylate (superglue) or acrylic resin, you could probably do plaster as well. The real problem is that the foam disintegrates if you just brush it with your finger, so fine detail has to be carefully preserved if you want that level of resolution.

Car engines and a lot of other cast metal uses a process called lost foam casting. AFAIK the foam plus a sprue is packed in sand mixed with some sort of bonding agent. After the sand is cured, the foam is burnt out in a furnace leaving a cavity with a negative impression. This machine would work great for that, even if the rest of the setup is impractical for individuals.

Now you have me wondering.
Could you use styrofoam and a hot needle in something like this. If you could some how heat a needle and us it like a hot wire cutter That way you could have a more durable and accurate model.

Penn State has a pretty sweet foundry setup where I used to do a lot of lost foam casting as an IE student. We never used a binder on the sand or burned out the foam in a furnace. Basically we put the foam in a bucket, covered it with plain ol’ sand, and put it on a shaker table for a few minutes to settle the sand out. As you pour, the metal will vaporize the foam and fill the void. I can’t remember the accuracy we achieved with this method, but other types of sand casting can achieve +/- .020… not bad when you consider that’s the diameter of a single grain of sand.

You can spend the time burning the foam out before-hand, but that’s almost a wasted step (not to mention the cost of the binder you’re using). The main problem you run into with engine blocks and other large castings is all that foam-turned-gas needs to be properly vented. If your foam shape is designed to allow this, you’re golden.

derpa is correct. You lose resolution with a bigger bit.
The faster way to do it is to change bits, but that requires more programing/changing tools. You use a coarse bit to remove lots of material at once, then the fine bit to detail it.
I think the X/Y motor speed may be the reason for such a long cutting time, on an industrial CNC mill, this should complete in nearly a fifth of the time out of similar material.

Usually there are 2-3 passes:
– first a fast&rough one with a large bit, just to get the most of the material out of the way.
– then a slow&fine one with a small bit. This creates most of the detail
– sometimes another pass like contour or waterline for stuff with sharp edges